# File lib/zip/zip_extra_field.rb, line 105
      def merge(binstr)
        return if binstr.empty?
        size, content = initial_parse(binstr)
        # size: 0 for central directory. 4 for local header
        return if(!size || size == 0)
        uid, gid = content.unpack("vv")
        @uid ||= uid
        @gid ||= gid
      end